1. Field of the Invention
The invention pertains to a vibration damper.
2. Description of the Related Art
U.S. Pat. No. 6,651,787 discloses a vibration damper which fulfills the function of filtering out high-frequency, low-amplitude excitations and thus offers a comfort advantage over conventional vibration dampers. A first piston is fastened permanently to the piston rod. The second piston slides on the piston rod and is supported by two springs. One of these support springs rests against the first piston, whereas the second support spring rests against a spring plate, which is held in turn by a lock washer. The support springs pretension the valve disks against the second piston and also oppose the axial movement of the second piston. This design requires a complicated assembly procedure and also means that the pretension of the valve disks depends on the axial force which supports the second piston.
A vibration damper with a cylinder in which a piston rod is guided with freedom of axial movement is known from JP 10-339,345 A. A first piston is fastened permanently to the first piston rod, and a second piston is mounted with a certain freedom of movement in the axial direction. The second piston has elastic valve disks and can shift axially against the elastic force of springs. The cylinder has a working space on the piston rod side of the first piston, another working space on the side of the first piston opposite the piston rod, and a working space between the two pistons. Valve-equipped through-openings control the connection between the working spaces. This design also fails to provide a structural unit which can be preassembled for the second piston with its springs.